This study will examine the biomechanics of the hip in normal and dysplastic patients, specifically focusing on patients with "traditional" dysplasia versus those with a dysplastic retroverted acetabulum. Patient-specific finite element models will be used to predict contact areas, maximum cartilage stresses and maximum bone stresses and their locations for three patient groups (normal, traditional dysplastic, retroverted dysplastic). The rationale for this study stems from the fact that acetabular dysplasia may be the leading cause of premature osteoarthritis of the hip; however, the exact relationships between the altered geometries associated with different types of dysplasia and the resulting stresses in the joint are poorly understood. The literature that has examined the relationships between acetabular dysplasia and development of hip osteoarthritis is contradictory. The overall objective of this study is to elucidate the biomechanical differences in hip joint loading and stresses in patients with normal hips, "traditional" dysplastic hips and hips with dysplasia characterized by retroversion of the acetabulum during simulated single-leg stance and stair climbing. [unreadable] [unreadable] [unreadable]